This proposal has three parts: 1) a study of the epidemiology of AIDS in I.V. drug abusers, 2) a study of neuropsychological and personality function in HIV seropositive I.V. drug abusers, and 3) a study of their social networks aimed at obtaining data that may be used to develop interventions to reduce high risk behavior. The first study will evaluate the prevalence of seropositivity among a cohort of I.V. drug abusers both in and out of treatment in the Philadelphia area. It will obtain data allowing the assessment of the rates at which seronegatives become positive among subjects in both groups, and on the behaviors that are associated with this change. It will also provide data on the rate of disease progression is more common in individuals with certain demographic characteristics such as age, race, sex or treatment status. The second study will assess the epidemiology of neuropsychological dysfunction in HIV seropositive users, will characterize this dysfunction, will relate neuropsychological functioning to medical status, and will create a database to address future research questions in this area. The third study will obtain information about the social networks of I.V. drug abusers both in and out of treatment. Subjects selected for this study will be chosen from a cohort of those in the epidemiological study. This study will aim to define the social support networks of I.V. drug abusers to determine points of influence which may be useful in developing intervention programs that can alter and sustain change in high risk behavior. This study will fill a void in research on AIDS in intravenous drug abuse both generally and in the Philadelphia area. It will also provide a new and exciting initiative for our ongoing drug abuse research program, and will be coordinated through our Center for Research on the Treatment and Prevention of Intravenous Drug Abuse.